Optical photometer especially for photographic appliances



June 20, '1933, w- SCHUCHTER I 1,915,033

OPTICAL PHOTOMETER ESPECIALLY FOR PHOTOGRAPHIC APPLIANCES Filed DSC. 17.1951 jl Pub; Aff l Patented June 20, 1933 UNI'TED, STATES PATENT iOFFICE y rWILHELM scnLIcH'rER,` OFYFREIBURG, GERMANY OPTICAL PHTUMETERESPECIALLY FOR PHOTOGRAPHIC APPLIANCES Application iedmece'mbe'r i7,1931, serial No. 581,747, and in' Germanynecemb'er '16, 1930. I, y

An application -has been filed in Germany December 16, 1930. l VThisinvention relates to improvements 1n Aphotometers, one object of theinvention being toetl'ect improvements-in the construction of the meansfor damping the light, an. other object. being to provide means fortransferring the light raysffrom the opening in the plate in thefront-end of the main tube, which is eccentric, to. saidV plate -and atone edge thereof to a cross shaped opening in the'center of anotheropaque disc, and which corresponds vWit-l1 the `optical axis, anotherObject being to leffect improvement-s in the construction andarrangement of the scales for measuring the intensity of the light anddetermining the exposure time.

lith the above and other objects in view, the invention consists in thelconstruction, combination and arrangement of devices hereinafterdescribed and claimed.

In the accompanying drawing Figure 1 is a central longitudinal sectionalview cfa photometer illustrating the prior art. -v

Figure 2 is a similar View showing a detail of the construction of thesame.

Figure Sisa detail clevationof the dalnpening device.

Figure 4 is a snnilar View of the plate forarrangement' in the front ofthe main tube and' having the eccentricallv arranged opening for theadmission of light.

Figure 5 is a similar view of the second opaque. disc having thecontrasting sign.

n Figure 6 is a central longitudinal sectional view of a photon'ieterconstructed and arranged in accordance with this invention.

Figure 7` is a detail elcvationof the metallic disc having the crossshaped central opening forming the sign.

Figure 8 is a detail sectional perspective of the improved light dampingdevice-forming in effecta rascade diaphragm.

l Figure 9is a detail central longitudinal section of the main 4tubegandthe rotatable cap and the means for locking said members togetheragainstcasual movement While they capV is being turnedstep by step onthe main tube in the operation of the scales fordearrow from the spaceor chamber containing the photographic object and which llight enterssaid tube. These rays oflight are transmitted through a light dampingAdevice 23 to a second opaque disc' 24 provided in the interior of theinstrument and on which is provided a contrast-sign which may be sightedby the ocular 25 placed in the chief tubeI 21. The light damping device23 is usually combined with a revoluble exterior adj ustingring26'placed on the main tube 21 70 so that the sign-mounted Within thepath of the'range of vision 24 may be darkened and brought toextinguishment by the rotation of said ring. The' more luminous thelight which falls on the' front opaque disc 22, the 75 greater will bethe necessity to diminish the' light at this end and the adjusting ofthering26 in the point of extinguishment of the sign isexactlysubordinated tothe vaille of light which must be measured.lCirculating-'d scales, such' as 27 and 28 which are rotatably or rigidlyfitted on the main tube 2l', have for object to enter into thecalculating operation or moment other factors influencing" the period ofexposure such as the sensibility of E55@-l the, photographic plates andof the dia# phragm, so that the time of exposure can be read on oneofthe scales. Constructional dif-4 ficulties of such photometers rise inthe necessity of providing a favorable light damping appliance. Owing tothe concentric disposition of the whole instrument With reference to theoptical axis, it seemsto be obvious to utilize a light. dampingappliance which con-4 tracts itself concen'tricall) to the `opticalaxis, 95

for instance an iris-diaphragm. Hoivever it has beeniound that thelatter is not suitable for the purpose because it has-.-in view of thetube. diameter of 2 cln--av too small meas- -uring sphere, so that ithas ybeen 4necessary 100 to enlarge the measuring sphere by insertingfurther damping means, for instance the addition of a supporting devicehaving fields of different transparency which has again the disadvantageof a complicated operation and which endangers the exactness of themeasuring result if the different measuring spheres do not constantly orcontinually run the one into the other. A further disadvantage incidentto the use of the iris-diaphragm'and other similar concentricallycontracting diaphragms resides in the fact that different rotatingangles are necessary to obtain the same darkening relation, that is at agreater aperture a greater angle than at a smaller, so that theadjusting scale of the ring 26 would be irregular and the arrangement ofa calculating scale with equidistant divisions would be impossible.

The construction of the photometer becomes much more favorable, if there4is used for light-darkening or damping a constructional organ or deviceof circular section whose light-damping elements are disposed on theborder zone which is turned passing behind an opening `provided in theborder zone of a rigid plate, damping thus uniformly the light enteringthrough the said opening in conformity with the rotatm angle. Such anarrangement isshown 1n Fig. 2, 1n

which only the front part of the instrument is.

represented. The'main tube 29 is closed in front by a plate 30 having aneccentrically arranged opening 3l (Figs. 2 and 4). On

the main tube 29 rotates a projecting cap 32 in which is fitted acircularplate 33 on which a circular opaque disc -34 closely bears. Fromthe opening 31 a channel 35. is directed to the second opaque disc 36(Figs. 2- and 5) on which is provided within the area, determined by theend of the channel 35, the contrasting sign 37, forming a circular.field or point which is divided into two Selm-circles of differentclearness or luminosity. Within the border zone 38 of the disc 33 (Fig.3) are provided the light-damping elements as shown in Fi 3, comprisinga spiral-like slot or a series o apertures or bores of decreasingdiameter or an absorbing covering having a progressively or graduatedincreasing' absorbtion power and the like, so that 'at a rotation of thecap 32 the-light lentering through the opening 31 is damped measurably;the sign 37 becomes thus darker and darker and finally disappears as thetwo semicircles of different clearness run together.

Whatever light damping elements may be used within 'the border 38 of thedisc 33,

there exists always the great advantage that it is principallypossible-when choosing the exactly appropriate light damping deviceswithin the border zone 38-to cover the total photographic measuringsphere by only one `rotation, with the help of a logarithmicallyequidistant division, which allows a. very simple manipulation of thephotometer (see also the German Patent No. 460,889).

These several advantages however are accompanied by a singledisadvantage. The light damping effect within the border Zone has theconsequence that the radiancy is not l placed on the line of the opticalaxis, and hence the sign 37 must be located cccentrically and on theborder of the range of vision. While in all other optical instrumentsone is accustomed to observe the critical optical phenomenon in thecenter of the visionrange, that is on the optical axis, it is necessaryin the optical photometer shown in Fig. 2 to direct the sightoblique-angled towards the top. This is not only inopportuno but alsodoubtful as to the exactness of measuring. It is known that the retinahas a different sensibility on the border, than in the center, so thatthe measuring result and the extinguishing moment are different for aneye which looks in an oblique-angled direc.

tion towards the top, than for one which looks in a straight horizontalline.

Therefore a certain dexterity and experience are necessary in order toobtain always uniform results with the help of a photometer Whosecontrast-sign becomes visible on the border and the inexperienced novicebecomes perplexed when the sign which has disappeared when lookingtowards the top, reappears when he looks accidently or temporarily inthe direction of the optical axis.

The object of the present invention is to provide an opticallight-measuring instru- 1 ment, having the special characteristics of aphotometer, in which the contrasting sign is located centrally withinthe vision range, i. e. on the optical axis, without abandoning the mostimportant advantages of a light-damp- 'i ing appliance producing itseffects on the border-zone. This result is realized by the fact that thelight passing through the border-sphere of the light damping device isdeflected by afdouble reflection towards the optical axis andtransferred to the central part of the vision-range on which the sign islocated.

A specially practical form of embodiment of the photometer is showninthe following figures. Fig. 6 shows a longitudinal, vertical sectionof the instrument. The main tube 39 is closed in front by a cylindricalmember l 4,9, whose bottom 4l has an eccentrically arranged opening 42and a riveted central stud 43 on which is fitted a circular plate 44whose aperture 45 corresponds to the said opening 42. The cap 46 whichmay rotate on the main tube 39 is connected by a screw with thelightdamping device 48 which can rotate within the chamber formed on theone side by the bottom 41 of the member 40 and on the other side by theplate 44, while the border sphere or zone bearing the light-dampingelements passes between the two apertures or windows ll-'Z and 45. Theopaque disc 49 bears-on a recess of the rotating tube 46 and is held inthis position by a closing ring 50. Vithin the member' 4() is placed.close to the bottom 4l a metal sheet 5l, having a tongue 52 Which isbent at an angle of 45'with respect tothe optical axis. On the ring 53which bears on the .metallic sheet 51, is placed a second metallic sheet54 having a tongue 55which is parallclto and spaced from thesaid tongue52. The said metallic sheet 54, provided with a ciicular opening 56. Anopaque disc 5T bears against the sheet 54. and a metallic discl 5S (Fig.7), bears against t-lie opaque disc 23 and lhas in its cent-er anopening in the forni of a cross 59. which serves as the sign mentionedhereabove` and which when observed through the ocular 6() movable withinthe main tube 39, contrasts luininously on` a dark ground when theopaque disc 57 is lighted from theleft hand. y

'l`hc metallic faces 52 and 55 serve to deflect the light striking uponthe opaque disc t9 in the direction of thearrow,'after havingpasscdthrongh the opening of the revoluhle light-damping appliance 48and through the opening 42 towards the optical axis.'aiid to transferthis light to the centrally disposed sign 59. y

As the matter in question. is dispersed light, it is not necessary thatthe surface 52 and acting as reflectors be mirrorlike. ll'hite surfaces,reflecting in a diffused manner. for instance surfaces having alustreless` mat paint can be used. The said surfaces can valso be madeof aluminium rendei-ed lustrelcss by .brushing or corrosive agents. p

(il and 62 are scale-rings taking into consideration the diaphragm andthe sensibility of the photographic plate,'thc most advantageousinscriptions and arrangements of which are hereinafter described.

The damping device provided on the border sphere may be. variouslyconstructed.

There may be used series of apertures of decreasing diameter, slots ofdiminishing section, angular shaped apertures covered by a grey film ofcontinuously or graduately increasing absorbtion power, or some otherdamping means or combinations thereof.

Such a. light damping device may be stationary ormovable. It is possible'to obtain only a limited light damping effect by means of a range orseries o f apertures of progressively decreasing diameter. If forconstructional reasons the greatest aperture must not exceed adetermined surface, this effect is limited by the diameter of thesmallest apertu're which is the last aperture of the range, and therequired lightrdamping effect can be obtained practically and withsufficient cxactness. Now, if a uniformly lightened mat surface isprojected on a parallel mat surface, through such a range of apertures,

a graduated light damping eect is produced on this second opaque disc,and if this damped effect is again projected in a similar manner by a.second lrange ofapertures on a third mat glass, there is again producedAa graduated light damping effect which corresponds to the sinn ofllogarit-hinical degradations of-thc two different ranges of the disc G4is provided a mat surface (SG shown in hatched lines. If it is supposedthat such adiaphragin is inserted in lieuoffthat 4b shown .inv Fig-'6,and rotated by'thefrd tatable cap 4G in the direction ofthe arrow, thelight' radiating from the mat glass ..49 through lthe opei'iings 45 and42 is more and more damped, in proportion to the increase of therotation angle, by means yof the dccreasing slot and the rangeV oflapertures (which .form its continuation) provided on the two discs 63and 64. i

yIf for instance the surface of the. passage opening` producing itseffect in the initial position, is f qmm, andif a total light dan'ipingeffectis required in the relation of 1600/1, this requirement isrealized by the fact that vthe surface of the last aperture of the rangeis chosen=l/40 f, because the lighting power o f the mat surface 6,6 isthus reduced on 1/40'of the initial luminosity, 1/40 j of this surfacebeing only effective, so' y that the resulting damping is=1/1600, whichit would not be 4possible to realize by one only rangev of aperturesbecause then the smallest aperture must be 1,/1600 f, while. theproduction of a range of apertures, with a largest and smallest siii'-face of respectively -lf and 0,1 qinn'i (corresponding to an aperture of0,4 min dtr.) offers no difficulty when using a perfect punch-v ingtool. The light .damping effect can be realized continuously orgradually. The continual dampingrould be obtained. under the pres-v entcircinnstances at an equal measuring range or sphere, for instance by aS-graduate fcascade diaphragm, wherein the damping effect of each gradeis effected by means of a slot becoming more and more contracted ,tofward one end. Practice has however shown that a graduate darkening ismore favorable,4

because t-lie sign observed in the range of vision then becomes darkerby graduation and extinguishes also in the same manner, sothat thecriterion of adjusting becomes also more apparent for persons notacquainted with the .effect art. It is of no importance if there areused in this case continuously or gradually acting light darn ino'elements on the border zone of the lig t darkening device, but it isimportantin this direction that the rotation movement of the lightdamping device or the rotative tube acting on it be constructed in sucha way that it grasps into 'arresting points, so that at this graspinginto the arresting points, determined light 'damping grades are passedwhich must be determined in such a way that there results therefrom amost nearly possible equidistant logarithmical scale of the exposuretimes.

The vkind of auxiliary means producing such arresting points, is of noespecial importance. A very simple, but accurate working device is shownin Fig. 9. Into the inner surface of the rotating tube 46 are cutgrooves 67 into which grasps during a rotation of said tube an elastictongue 68 which is bent outwardly from the front part of the main tube39 and when one of the aperturesl of the range of the disc 63 remains inits Stillstand in the center of the opening 45, the tube 46 is lockedagainst casual rotation.

The arresting movement of the rotating tube not only has the advantagethat the extinguishment of the sign discernible within the range ofvision takes place suddenly, hence marking in a more precise manner theadjusting point, but its consequence is a more simple and more suremanipulation of the exterior calculating scale, as will be understood.Fig. 10 shows the exterior arrangement of the photometer. On the smoothgraduated part 69 of the rotating tube 46 are directly engraved thefigures and fractions and decimals indicating the exposure-times.

The ring 61 on which are engraved the diaphragm 4figures (1, 4 1, 6-2and the index arrow 70, grasps with its elastic tongue 71 into thegrooves 72 of the ring 62 rigidly fixed on the main tube 39 andrbearingthe engraved Scheiner scale (27, 5-26-24,5

. etc.). If, before measuring or determining the exposure-time, the ring61 is placed with its index on the known Scheiner graduation figure (17for instance) the totaldisposition lof the scale is erfectly determinedand the reading 0E of) the exposure times for the different diaphragmecan be performed with great composure without fear of an involuntarydisplacement, because the rotating tube grasps also into an arrestinggroove at the moment of extinguishment of the sign (cross 59). It willbe understood that 1t is also possible to inversely provide thediaphragm scale on the tube 46 and the exposure .times on the ring 61within the scope of the invention.

.It will be understood from the foregoing that the exterior calculatingdisposition isl constituted by three reciprocatably displaceable scales,the first whereof, rigidly fixed in the chief tube, bears thesensitivity inscri tions, the second contiguous rotatable sca e ringwith its index being arrestable by grasping in grooves of thesensitivity scale, while the second and third scales, indicating theexposure time and the diaphragm opening, are graved on this second ringand on the outer adjusting tube grasping in arresting grooves, acting onthe light damping device, so that after havingr adjusted the sensitivityscale of the plates before the measuring operation, and after havingobtained the adjusting point defined by theextinguishment of the sign orcross, the totality of scales of the instrument is secured against aninvoluntary displacement.

I claim:

An optical instrument of the class described, having a tube provided inthe opposite ends with an objective and an opaque closure having aneccentrically arranged light admitting opening, a cascade diaphragmarranged for rotary movement in the tube and comprising a pair of spaceddiscs each provided with eccentrically arf ranged openings ofprogressively decreasing area in the direction of rotation of saiddiaphragm and the openings of the rearmost disc being covered withtranslucent material,

an opaque disc spaced from the said cascade diaphragm and having a signopening coincident with the optical axis of the instrument, and means todeflect light from the said cascade diaphragm to and through the signopening and into the optical axis.

In testimony whereof I have hereunto set my hand this third day ofDecember A. D.

- f. WILHELM SCHLICI-ITER.

